Physical and chemical characteristics of water and sediment of nine mountain astatic ponds (northern Apennines, Italy)

摘要

Temporary wetlands, common both in hot climates and in temperate northern Europe and North America (Williams 1987), fluctuate between dry and wet phases and, when filled, are probably little different physically and chemically from equivalent-sized permanent habitats (Boulton & Brock. 1999). Rocky pools, intertidal ponds, playa lakes and oxbow lakes are all heterogeneous examples of astatic biotopes characterised by different geographic position, size, salinity, hydroperiod and water renewal, all factors that hardly permit these ecosystems to be grouped into a general classification. However, temporary water bodies are usually shallow, with a large surface area to volume ratio, and for this reason show hydrologi-cal characteristics very susceptible to weather fluctuations and surficial sediment metabolism (Bron-mark & Hansson 1998). In temporary ponds the main changes in hydrochemical parameters usually coincide with the desiccation period, due to water evaporation and the small water volume remaining (Boulton & Brock 1999), and with the wetland refilling after dry periods because of the flush of dissolved materials and their release from sediments (Hartland-Rowe 1966, Barlocher et al. 1978, DIaz-Espejo et al. 1999). During wet phases, nutrient concentration normally depends on organic matter input/sedimentation and microbial processes of mineralization, sediment water fluxes and assimila-tion rates by primary producers (Ponnamperuna 1984).